EmmaC, had not realised so not to worry, look at
http://www.straws.com/orthoses.htm - they are basically inserted either above or below the insole of the running shoe and provide extra cushioning.
I got mine from a physio as they were the first people I went to see when I had my shinsplints, so that might be a good place to go, you can also get custom ones made up to fit the individual foot (extremely expensive).
When I got mine, they fixed the shinsplints straight away, but I had to stop wearing them as I was getting very bad blisters on the arches of my foot.
Hope this helps.